Terrorism and the uncertainty about who or what gets hit next have affected the United States in an unprecedented way, following the events of September 11. Analysts say even the business of Wall Street is different.

Historically, the U.S. stock market has reacted to scheduled events. In the Vietnam era, it was casualty counts, which were regularly timed releases. In the 1970s, it was the money supply. In the 1980s, traders on Wall Street say they waited for critical data on trade with Japan.

Today, Wall Street is tuned to news related to terrorism the bombing of targets in Afghanistan, the hunt for Osama bin Laden and the persistent trickle of anthrax cases in the United States. The difference now, however, is the immediacy of communication.

"What's interesting about this, and this is sort of a new twist, is that news is real-time and the events are real-time," said Michael Balog, an analyst with Banc of America Securities. "You never know when you're going to get a piece of good news or bad news. But the market certainly expects a lot of bad news every day and watches for it with bated breath."

Patrick Boyle from the Credit Suisse First Boston brokerage says this is the most difficult market he has ever encountered in his decade of professional stock trading. "It's such a day-to-day trading event. Every day is different," he said. "You're just watching and listening to all the information that comes across the desk. You just don't know what's going to come across the TV."

The financial markets have never taken well to uncertainty of any kind. But Wall Street experts say September 11 added a new dimension to the unknown. With officials in Washington talking about a war on terrorism that could last a long time, investors may have to get used to living with uncertainty defined by a lot more than the ups and downs of the U.S. economy.

Some investors have abandoned the markets, moving their money to the sidelines for now. But many are hanging in for the long-term, shifting nervously from one sector to another. Analyst Michael Baylog says choosing safe stocks today is a big debate, and the correct choice is anybody's guess.

"Household products, on one hand, are safer and more defensive," suggests Mr. Baylog. "On the other hand, the technology stocks . . . but as one trader said to me, I don't know what's going to happen."

The U.S. central bank's policy this year of easing credit and the anticipation of an economic stimulus package from Washington have raised hopes for a turnaround in the American economy. But just when that will happen again falls into the category of the unknown. Experts say next year. But they are divided on exactly when next year. Too many opinions, too many different predictions, are shadowing the business of Wall Street.